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Highly‐polarized emission provided by giant optical orientation of exciton spins in lead halide perovskite crystals
(2024-06-17) Kopteva, Nataliia E.; Yakovlev, Dmitri R.; Yalcin, Eyüp; Akimov, Ilya A.; Nestoklon, Mikhail O.; Glazov, Mikhail M.; Kotur, Mladen; Kudlacik, Dennis; Zhukov, Evgeny A.; Kirstein, Erik; Hordiichuk, Oleh; Dirin, Dmitry N.; Kovalenko, Makysm V.; Bayer, Manfred
Quantum technologic and spintronic applications require reliable material platforms that enable significant and long-living spin polarization of excitations, the ability to manipulate it optically in external fields, and the possibility to implement quantum correlations between spins, i.e., entanglement. Here it is demonstrated that these conditions are met in bulk crystals of lead halide perovskites. A giant optical orientation of 85% of excitons, approaching the ultimate limit of unity, in FA0.9Cs0.1PbI2.8Br0.2 crystals is reported. The exciton spin orientation is maintained during the exciton lifetime of 55 ps resulting in high circular polarization of the exciton emission. The optical orientation is robust to detuning of the excitation energy up to 0.3 eV above the exciton resonance and remains larger than 20% up to detunings of 0.9 eV. It evidences pure chiral selection rules and suppressed spin relaxation of electrons and holes, even with large kinetic energies. The exciton and electron–hole recombinations are distinguished by means of the spin dynamics detected via coherent spin quantum beats in magnetic field. Further, electron–hole spin correlations are demonstrated through linear polarization beats after circularly polarized excitation. These findings are supported by atomistic calculations. All-in-all, the results establish lead halide perovskite semiconductors as suitable platform for quantum technologies.
Influence of changing loading directions on damage in sheet metal forming
(2024-03-12) Lennemann, Philipp; Korkolis, Yannis P.; Tekkaya, A. Erman
The impact of the stress state on damage evolution, fracture behavior, and product performance is well understood for proportional loading. However, many complex sheet forming operations involve non-proportional loading, which affect the material's hardening and fracture characteristics. This study investigates the influence of a loading direction change on damage evolution in a dual phase steel DP800. Specimens are pre-strained by tensile tests and subsequently loaded in either the same or orthogonal direction to the initial pre-strain direction by additional tensile tests and bending tests. Damage quantification by scanning electron microscopy reveals lower damage evolution after an orthogonal change of loading direction in contrast to monotonic loading directions. The load paths, defined as a history of triaxiality and Lode parameter during loading, are identified numerically under consideration of kinematic hardening. Since kinematic hardening leads to higher triaxialities after orthogonal changes, the load path is not the dominant influence on damage. A possible explanation for the experimental results is the void characteristics after tensile load. After the pre-straining in tensile test, voids are oriented orthogonally to the tensile direction and located between hard martensitic phases. The influence of this morphology on subsequent void growth is illustrated by a simulation verifying that an orthogonal change of loading direction results in void shrinkage, while monotonic loading directions lead to further void growth.
DSC reveals the excipient impact on aggregation propensity of pharmaceutical peptides during freezing
(2024-11-01) Zäh, Maximilian; Brandenbusch, Christoph; Artusio, Fiora; Sadowski, Gabriele; Pisano, Roberto
Pharmaceutical peptides are susceptible to aggregation in solution, making stabilization by addition of suitable excipients essential. To investigate this stabilization, lengthy and cost-intensive experiments are often necessary. In this work, a differential scanning calorimetry (DSC) based method was developed that allows a rapid assessment of the stabilization properties of excipients regarding the aggregation of pharmaceutical peptides. The stabilization properties of investigated excipients are derived from the thermal behavior around Tg', the glass-transition temperature of the excipient-rich phase after freezing, as a function of repeated freeze-thaw cycles.
The pharmaceutical peptide glucagon was investigated in combination with the excipients trehalose and lactose. In addition to the type of excipient, the concentration ratio of peptide/excipient was also varied. Lactose proved to better stabilize glucagon solutions compared to trehalose. On the one hand, the onset of aggregation could be delayed and after aggregation started the aggregation kinetics were slowed down. In addition, it was shown that a high excipient to peptide ratio, regardless of the type of excipient tested, reduces the aggregation tendency of glucagon.
Metabolic bottlenecks of Pseudomonas taiwanensis VLB120 during growth on d-xylose via the Weimberg pathway
(2024-06-06) Nerke, Philipp; Korb, Jonas; Haala, Frederick; Hubmann, Georg; Lütz, Stephan
The microbial production of value-added chemicals from renewable feedstocks is an important step towards a sustainable, bio-based economy. Therefore, microbes need to efficiently utilize lignocellulosic biomass and its dominant constituents, such as d-xylose. Pseudomonas taiwanensis VLB120 assimilates d-xylose via the five-step Weimberg pathway. However, the knowledge about the metabolic constraints of the Weimberg pathway, i.e., its regulation, dynamics, and metabolite fluxes, is limited, which hampers the optimization and implementation of this pathway for bioprocesses. We characterized the Weimberg pathway activity of P. taiwanensis VLB120 in terms of biomass growth and the dynamics of pathway intermediates. In batch cultivations, we found excessive accumulation of the intermediates d-xylonolactone and d-xylonate, indicating bottlenecks in d-xylonolactone hydrolysis and d-xylonate uptake. Moreover, the intermediate accumulation was highly dependent on the concentration of d-xylose and the extracellular pH. To encounter the apparent bottlenecks, we identified and overexpressed two genes coding for putative endogenous xylonolactonases PVLB_05820 and PVLB_12345. Compared to the control strain, the overexpression of PVLB_12345 resulted in an increased growth rate and biomass generation of up to 30 % and 100 %, respectively. Next, d-xylonate accumulation was decreased by overexpressing two newly identified d-xylonate transporter genes, PVLB_18545 and gntP (PVLB_13665). Finally, we combined xylonolactonase overexpression with enhanced uptake of d-xylonate by knocking out the gntP repressor gene gntR (PVLB_13655) and increased the growth rate and biomass yield by 50 % and 24 % in stirred-tank bioreactors, respectively. Our study contributes to the fundamental knowledge of the Weimberg pathway in pseudomonads and demonstrates how to encounter the metabolic bottlenecks of the Weimberg pathway to advance strain developments and cell factory design for bioprocesses on renewable feedstocks.
Untersuchung des Schlupfverhaltens von Reibrollenantrieben in Elektrohängebahnen (EHB)
(2025) Wißuwa, Manuel; Künne, Bernd; Noche, Bernd
Die weltweite Globalisierung und der zunehmende Kostendruck in der Logistik zwingen die Unternehmen, ihre internen Transportprozesse zu optimieren. Die Transportkosten machen oft einen erheblichen Teil der Logistikkosten aus und beeinflussen somit direkt die Rentabilität. Die Optimierung des innerbetrieblichen Transports wird daher immer wichtiger. Insbesondere bei geringen Mengen besteht diesbezüglich entsprechendes Optimierungspotential, da sich mit bisherigen Technologien eine Automatisierung wirtschaftlich nicht rentiert hätte. Vollautomatische und autonome Elektrohängebahnen bieten eine Möglichkeit, diese Lücke zu schließen, indem sie kleine Güter kostengünstig und effizient über längere Strecken transportieren.
Der Stand der Technik zeigt, dass autonome, selbstfahrende und selbstagierende Elektrohängebahnsysteme für kleine Lasten im Bereich der innerbetrieblichen Logistik nicht zu wirtschaftlich vertretbaren Preisen auf dem Markt verfügbar sind. Ziel dieser Arbeit ist es gewesen, die Machbarkeit des Einsatzes des Elektrohängebahnsystems unter verschiedenen Bedingungen zu demonstrieren, die Grenzen des Systems zu ermitteln, die Wirtschaftlichkeit zu untersuchen und eine Grundlage für zukünftige Entwicklungsarbeiten aufzuzeigen.
In den durchgeführten Versuchen wird die grundsätzliche Machbarkeit des Elektrohängebahnsystems unter verschiedenen Bedingungen geprüft. Dazu gehören Testfahrten auf verschiedenen Stahlprofilschienen und einem Polyesterseil unter Berücksichtigung von Steigungen, Kurven und Weichen in Rundkursversuchen. Weiterhin sollen Schlupfversuche mit drei verschiedenen Laufrad- und Schienenkonfigurationen (Rechteckprofil, Flachprofil und Seil) durchgeführt und detaillierte Messwerte ermittelt werden. Die Auswertung dieser Versuche konzentriert sich auf die Berechnung des Schlupfes und den Vergleich dieser Werte. Daraus können Rückschlüsse gezogen werden, welche Steigungen befahren werden können und welche Laufradkonfigurationen am besten geeignet sind. Darüber hinaus werden Steigungsversuche am vertikalen Seil durchgeführt, bei denen Faktoren wie Umschlingungswinkel, Seilspannung und verschiedene Gewichtsbelastungen berücksichtigt werden. Ziel dieser Versuche ist es, die Machbarkeit verschiedener Kombinationen der eben genannten Einflussfaktoren zu ermitteln und praktische Empfehlungen für deren Einsatz zu geben.
Die Ergebnisse der Versuche belegen die generelle Machbarkeit des Einsatzes des Elektrohängebahnsystems in der innerbetrieblichen Logistik. Die Grenzen des Systems liegen unter anderem im Bereich der Steigungswinkel und dem daraus resultierenden instabilen Fahrverhalten. Die wirtschaftliche Betrachtung bestätigt zudem eine attraktive Kostenstruktur für den betrieblichen Einsatz bei gleichzeitig hoher Flexibilität in der Streckenführung.
Die Ergebnisse und Erkenntnisse dieser Arbeit sind die ersten Schritte für die Weiterentwicklung des Elektrohängebahnsystems und dienen als Grundlage für zukünftige Entwicklungsarbeiten.